Search

Small polymeric ducts incorporating a ribbon-shaped mat of densely packed magnetic nanofibers have been manufactured via electrospinning by using a cylindrical manifold, alternately under rotation or static. The magnetic nanofibers mat is located on the side of the tube and aligned to the longitudinal axis using the assistance of a magnetic field. The designed methodology ensures that the magnetic particles are completely wrapped into a protective polymer shell. Experimental results demonstrate that the innovative confinement of magnetic nanofibers, forming a longitudinal ribbon on a tube side, confers a high and reversible transverse strain under a moderate magnetic field stimulus: a magnetic field gradient ≤30 mT/mm, at a basic field intensity

Magnetic field assisted electrospinning is supplemented by conductive sheets that envelop the magnets and have the same potential as the deposition electrode. By optimizing the experimental conditions, it is possible to produce wires made of polymer nanofibers that incorporate longitudinally oriented magnetic particles. The morphological and magnetic characterizations confirm the preferential orientations. The new nanofiber wires are easily aligned along the maximum intensity line of the applied magnetic field. Moreover, the nanostructured wires have high longitudinal elastomagnetic strain and high transversal deflection as a response to magnetic field stimuli. Therefore, these new threadlike aggregates of magnetic nanofibers could be very appealing for application in all microelectronic or biomedical devices whose functionality requires orientation or deformation.

Electrospinning technique has been successfully used to produce composite nanofibers combining magnetic nanoparticles with polymer matrices. Process conditions to assembly nanofibers in tubular systems, as well as their morphological and elastomagnetic properties, have been explored. A volume percentage of magnetic charge close to 30% has been achieved. The optimization of the fabrication method ensures that the particles are completely covered by a thin polymer shell, so safe-guarding bio-compatibility. In particular, the deformation induced by the direct elastomagnetic effect, applying a static or a pulsed magnetic field, has been investigated. Resultant devices exhibit good elastomagnetic stretchability at room temperature-longitudinal relative strain/exciting field ~4·10–3/(1.5·104 A/m) –, thus suggesting their potential use for applications in biomedical field as magneto-active components, as well as sensors and actuators.

Elastomagnetic effect (strain induced by magnetic field application) and piezoresistivity (change of electron conductivity due to an induced strain) are coupled in composite materials constituted by magnetic and conductive microparticles into an elastic matrix. On the basis of these effects, the principle of a new method to read magnetization direction changes, in a random sequence, is proposed and experimentally demonstrated. We have produced new composite magnetopiezoresistive samples, constituted of thin chip shaped Fe microparticles inside a silicone matrix, which under an applied magnetic field along their longitudinal axis, undergo an induced strain depending on the local magnetization direction. The resulting resistivity change can be easily detected and used to deduce the local magnetization direction. The magnetization and strain processes are reversible so that after the removal of external magnetizing field the sample is ready for new measurements. A demonstrator prototype has been conceived, produced and tested. The experimental results provide interesting data encouraging to continue the research towards nano-scale devices in order to pursue the intriguing perspective to achieve a magnetic field gradient sensitivity able to reveal magnetization of semipermanent nanomagnets, polarized ‘up’ and ‘down’.

We demonstrate that the average size and the size distribution of nanoparticles produced by ultrashort laser ablation in vacuum can be modified by irradiation of the nanoparticles' plume during its vacuum expansion with a nanosecond, UV laser pulse. The experimental results are interpreted by means of a simple analytical model of the laser-particle interaction, heating and vaporization. This technique thus shows to be a simple and general way to control, in vacuum, the average size and distribution of nanoparticles of different elements. [ABSTRACT FROM AUTHOR]